Loudspeaker and method for the preparation thereof

ABSTRACT

A loudspeaker in which the input resistance is improved and the effect of humidity on the playback frequency response is suppressed, and a method for the preparation of the loudspeaker. A sheet-like product, containing glass particles with a particle size of 8 nm to 300 nm and polyamide resin, and prepared by application of a paper-making technique, is used as the diaphragm. The content of the glass particles in the compound material is 5 weight % to 70 weight %. In preparing the diaphragm, a phase of an aqueous solution containing diamine and water glass is contacted with a phase of an organic solution containing a dicarboxylic acid halide to generate a compound material containing glass particles and the polyamide resin. The compound material so prepared is formed into a sheet by a paper-making technique. In the process of the preparation by the paper-making technique, the compound material mixed with other fibrous material may also be used as a starting material.

RELATED APPLICATION DATA

[0001] The present invention claims priority to Japanese Application No.P2000-117218 filed Apr. 13, 2000, which application is incorporatedherein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a novel loudspeaker employing acompound material of a polyamide resin and glass particles for adiaphragm, and a method for the preparation thereof.

[0004] 2. Description of Related Art

[0005] Recently, as the acoustic equipment, such as audio amplifier, isimproved in performance, large level signals (large input) are liable tobe applied to the loudspeaker, so that a demand is raised for improvingits input resistance.

[0006] If a large input is applied to a loudspeaker, there is evolvedheat in a voice coil section driving the diaphragm, thus thermallydamaging the diaphragm. For example, polypropylene, so far usedperferentially as a diaphragm material, has a thermal deformationtemperature as low as approximately 100° C. (ASTM D648: 0.455 MPa), andhence a problem is raised that the diaphragm made of polypropylene isdeformed by the large input, thus possibly destructing the loudspeaker.

[0007] By way of a countermeasure therefor, there is proposed adiaphragm for a loudspeaker employing a polyimide based resin, as ahighly heat-resistant material, a liquid crystal polymer, or aheat-resistant resin, such as polyetherketone resin.

[0008] However, the high thermal resistance indicates formingdifficulties, thus possibly leading to the lowering of productivity andto the increased manufacturing cost. Moreover, the material itself isexpensive, thus leading to increased overall cost.

[0009] For resolving the above problem, such a diaphragm is proposedwhich employs a polyamide resin having a higher thermal deformationtemperature of approximately 190° C., or a compound material formed ofthe polyamide resin admixed with inorganic fillers, such as glassfibers, carbon fibers, mica powders or calcium carbonate.

[0010] In these materials, the heat-related problems are resolved.However, there is presented such a problem that, due to significantchanges in the modulus of elasticity caused by hygroscopicity proper tothe amide resin, the playback frequency response of the loudspeakeremploying these materials for the diaphragm is changed significantlybetween that in the dry state and that in the humid state.

SUMMARY OF THE INVENTION

[0011] It is therefore an object of the present invention to provide aloudspeaker having superior input resistance properties and superiormoisture-proofness and which is not prone to destruction even under alarge input such that the replay frequency response is not affected byhumidity.

[0012] The present inventors have conducted eager researches, and foundthat the above object can be accomplished by using a homogeneouscomposite consisting of microscopic glass particles and a polyamide typeresin, obtained by polyamide synthesis in the presence of water glass,as an acoustic diaphragm. This finding has led to completion of thepresent invention.

[0013] In one aspect, the present invention provides a diaphragm for aloudspeaker including a compound material containing glass particleshaving a particle size of 8 to 300 nm and a polyamide resin, in whichthe compound material is a sheet-like member formed by a paper-makingtechnique.

[0014] In another aspect, the present invention provides a method forthe preparation of a diaphragm for a loudspeaker including contacting aphase of an aqueous solution containing a diamine and water glass and aphase of an organic solution containing a dicarboxylic acid halide togenerate a compound material containing glass particles and a polyamideresin, and forming the resulting compound material to the shape of adiaphragm by application of a paper-making technique.

[0015] The polyamide resin has a higher thermal deformation temperatureand satisfactory castability. However, if used alone, the polyamideresin undergoes marked change in the modulus of elasticity due to itshygroscopicity.

[0016] On the other hand, with a glass/polyamide compound material, inwhich extremely fine glass particles are homogeneously dispersed in thepolyamide, these changes in the modulus of elasticity caused by moistureabsorption may be eliminated to assure high thermal resistance and onlyslight lowering of the physical properties ascribable to moistureabsorption.

[0017] Therefore, in a speaker employing this compound material as adiaphragm, the input resistance is improved, while the reproducingfrequency response is not affected by humidity.

[0018] Moreover, in the compound material obtained on contacting theaqueous solution containing the diamine and water glass and the organicsolution containing the dicarboxylic acid halide, the glass particlesare homogeneously dispersed in the fibrous polyamide resin, such that itcan be readily formed to the shape of a diaphragm by the customarypaper-making method.

[0019] That is, according to the present invention, employing asheet-like material, mainly composed of a compound material composed ofextremely fine glass particles are homogeneously dispersed in thepolyamide, as a diaphragm, the input resistance and themoisture-proofness can be improved appreciably.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a graph showing temperature characteristics of themodulus of elasticity of a glass/polyamide compound material and apolypropylene/mica compound material.

[0021]FIG. 2 is a graph showing playback frequency characteristicsbefore and after moisture absorption of a loudspeaker employing a sheetof a glass/polyamide compound material prepared by a paper-makingtechnique and a loudspeaker employing a sheet of a polyamide componentprepared by the paper-making technique.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] Referring to the drawings, a loudspeaker and a method for thepreparation thereof, according to the present invention, will beexplained in detail.

[0023] The loudspeaker of the present invention employs a polyamideresin, containing glass particles, referred to below as aglass/polyamide compound material, is used as a material for thediaphragm, and a sheet thereof prepared by the paper-making technique isused as a diaphragm.

[0024] The glass particles contained in this glass/polyamide compoundmaterial are of extremely small size, with the particle size being 8 to300 nm. If the particle size of the glass particles is coarse-sized,being larger than 300 nm, the effect in improving moisture-proofnessfalls short, while adhesion to the polyamide resin also falls short,thus presenting a problem of exfoliation.

[0025] The content of the glass particles in the above-mentionedglass/polyamide compound material is preferably 5 weight % to 7 weight%. If the content of the glass particles is less than 5 weight %, themeritorious effect of adding the glass particles, such as moisture-proofproperty, is in shortage. If conversely the content of the glassparticles exceeds 70 weight %, the physical properties of the glassbecome dominant, such that the problem of brittleness is presented whenthe compound material is used as a diaphragm. Moreover, if the contentof the glass particles is excessive, the inter-fiber interaction of theglass/polyamide compound material is lowered such that physicalproperties tend to be lowered when the compound material is formed to asheet by the paper-making technique.

[0026] The glass/polyamide compound material is obtained as a fibrousproduct, which may be formed into a sheet by a paper-making technique inthe same way as in forming the fibrid to produce a diaphragm of thedesired shape.

[0027] In this case, the glass/polyamide compound material may be usedsingly and formed into a sheet by the paper-makingtechnique.Alternatively, the glass/polyamide compound material may be mixed withother fibers, such as fibrid, by the paper-making technique, to form asheet.

[0028] In the latter case, the proportion of the glass/polyamidecompound material is preferably 5 weight % or more. If the proportion ofthe glass/polyamide compound material is less than 5 weight %, thischaracteristic cannot be exploited sufficiently.

[0029] The glass/polyamide compound material, used as the diaphragmmaterial in the present invention, is suited as a diaphragm since it hassuch characteristics that

[0030] (1) the matrix resin is a polyamide resin and hence has highthermal resistance;

[0031] (2) the lowering of the modulus of elasticity is small because ofthe presence of ultra-fine glass particles of 8 to 300 nm in particlesize compounded therein;

[0032] (3) since the glass/polyamide compound material is fibrous innature, the paper-making technique, used extensively in themanufacturing process for a paper diaphragm, can be applied; and that

[0033] (4) the glass/polyamide compound material can be formed into asheet with a variety of fibrous materials such that it is possible toadjust physical properties, such as modulus of elasticity, required inthe designing of a loudspeaker.

[0034] Since the glass/polyamide compound material has high thermalresistance and suffers from only limited lowering of physical propertiescaused by moisture absorption, input resistance can be improvedappreciably by employingthis compound material as the loudspeaker.Moreover, reproducing frequency characteristics can be prevented frombeing affected by humidity, thus significantly improving moisture-proofproperty.

[0035] The manufacturing method for the loudspeaker and in particularthat for the diaphragm are hereinafter explained.

[0036] For preparing a diaphragm used for a loudspeaker of the presentinvention, it is necessary to synthesize the aforementionedglass/polyamide compound material.

[0037] For producing the glass/polyamide compound material comprisingglass particles homogeneously dispersed in the polyamide resin, it issufficient if water glass is caused to co-exist in the phase of theaqueous solution by a so-called interfacial polycondensation reaction inwhich monomers are reacted on the interface of a phase of an aqueoussolution and a phase of an organic solution.

[0038] Specifically, a solution of an aqueous solution composedessentially of a diamine and water glass (solution A) and a phase of anorganic solution composed essentially of a dicarboxylic acid halide andan organic solvent (solution B) are contacted to produce aglass/polyamide compound material in a fibrous morphology such as fibridform.

[0039] Among diamine monomers contained in the solution A, there arediamines having aliphatic chains, such as 1,3-diaminopropane,1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane,m-xylylenediamine or p-xylylenediamine, alicyclic diamines, such as2,5-norbornanediamine or 2,6-norbornane diamine, m-phenylenediamine,p-phenylene diamine, 1,5-diaminonaphthalene, 1,8-diaminonaphthalene,2,3-diaminonaphthalene, 3,4-diaminodiphenylether,4,4-diaminodiphenylether, 3,4-diaminodiphenylsulfone,4,4-diaminodiphenylsulfone, 3,4-diaminodiphenylmethane and4,4-diaminodiphenylmethane and a totality of aromatic diamines obtainedon substituting halogens, nitro groups or alkyl groups for one or morehydrogens of aromatic rings of the above compounds. Of these,1,6-diaminohexane, m-xylylenediamine and m-phenylenediamine arepreferred.

[0040] The water glass contained in the solution A is a water-solubleglass having a chemical composition represented by M₂O.nSiO₂, where M isan alkali metal. For example, water glass previously dissolved in water,such as water glass Nos. 1, 2, 3 and 4, stated for example in JIS(Japanese Industrial Standard) K1408-1950, in which M denotes sodium,with 1.2≦n≦4, may be used.

[0041] The concentration of water glass may be in a range from 2 to 100g/liter based on a solid content. The glass content in the compoundmaterial may be controlled by adjusting the concentration of waterglass.

[0042] For sufficiently promoting the polycondensation reaction, acidreceptors, such as sodium hydroxide, or surfactants, such as sodiumlauryl sulfate, may be added as necessary.

[0043] Among organic solvents contained in the solution B, toluene,xylene, methyl isobutyl ketone, chloroform, cyclohexane, cyclohexanoneor tetrahydrofuran, may be stated as being representative. Among thedicarboxylic acid halides, as monomers reacted with diamine monomers,adipoyl chloride, azelaoyl chloride, terephthaloyl chloride orisophthaloyl chloride, may be stated as being representative.

[0044] In the glass/polyamide compound material used in the presentinvention, the reaction of the water glass itself proceeds with theintroduction of the water glass to the polyamide as a result of contactbetween the solutions A and B, so that the glass is introducedhomogeneously into the polyamide as being high-quality silica type glasswith only small quantity of the alkali metal components.

[0045] The contact between the solutions A and B herein means both theinterfacial contact of the two without mixing and the contact withmixing.

[0046] The glass contained in the glass/polyamide compound material thussynthesized has a particle size as small as 8 to 300 nm and exhibitsoptimum adhesion. The glass content in the compound material may becontrolled by adjusting the concentration of the monomers or the waterglass.

[0047] By setting the monomer concentration in the solutions A and B to0.1 to 1.2 mol/liter, the glass/polyamide compound material can beproduced as a fibrous material with optimum amenability to apaper-making type manufacturing process. If a particulate compoundmaterial exhibiting no amenability to a paper-making type manufacturingprocess is produced, a fibrous material exhibiting amenability to apaper-making type manufacturing process can be obtained byco-precipitating the compound material and the pure polyamide from agood solvent therefor.

[0048] The fibrous glass/polyamide compound material, thus obtained, maydirectly be used for the paper-making like manufacturing method, as atechnique for producing the paper diaphragm, such that, similarly to theroutine paper diaphragm, a diaphragm of a desired shape can be formed bythe paper-making like manufacturing process.

[0049] It is possible to use only the glass/polyamide compound materialfor the paper-making like producing process, or this glass/polyamidecompound material may be mixed with other fibers, such as pulp, as astarting material for the paper-making like producing process.

EXAMPLE

[0050] The present invention is now explained with reference tospecified Examples, based on experimental results.

[0051] Synthesis of Glass/Polyamide Compound Material

[0052] To 27 g of water glass and 4.64 g of 1,6-diaminohexane was addeddistilled water at room temperature and the resulting mixture wasagitated to prepare 300 ml of a homogeneous transparent aqueoussolution.

[0053] To 7.32 g of adipoyl chloride was added toluene and the resultingmixture was agitated to prepare 200 ml of a homogeneous transparentorganic solution.

[0054] The above aqueous solution was charged into a 1-liter capacityblender vessel, manufactured by OSTERIZER INC. The above organicsolution was added to the aqueous solution in the blender vessel at 25°C., at a time, as the aqueous solution in the blender vessel wasagitated at an rpm of 10000 with an annexed agitation blade.

[0055] From the mixed solution was immediately precipitated a compoundmaterial in the form of white-colored fibrid. The agitation wascontinued for two minutes as the state of suspension was maintained.

[0056] After filtration, the precipitated fibrid were washed withboiling acetone and then with distilled water to produce fibrid of theglass/polyamide compound material.

[0057] The glass content was approximately 50 weight %, with theparticle size of the glass particles contained in the compound materialbeing 8 to 300 nm.

[0058] Similarly, a glass/polyamide compound material having the glasscontent of approximately 5 weight %, a glass/polyamide compound materialhaving the glass content of approximately 50 weight % and aglass/polyamide compound material having the glass content ofapproximately 70 weight % were produced in the above reaction system. Inthe following, these three sorts of the compound materials were used.

[0059] In the following, the glass/polyamide compound materials with theamounts of the glass of 5 weight %, 50 weight % and 70 weight % aretermed compound materials 1, 2 and 3, respectively.

[0060] Evaluation of Characteristics of Compound Materials

[0061] The compound material 2 produced was dispersed in water andformed by a paper-making technique into a sheet with a weight of 80g/m². Using a dynamic viscoelasticity measurement unit (RHEOVIBRONmanufactured by ORIENTEC INC.), evaluation was made of temperaturedependence of physical properties of the compound material 2.

[0062] For comparison sake, similar measurements were made of apolypropylene/mica compound material (proportion of mica: 30 weight %)preferentially used for a loudspeaker diaphragm.

[0063] The results are shown in FIG. 1.

[0064] As may be seen from FIG. 1, the polypropylene/mica compoundmaterial is significantly lowered in modulus of elasticity at atemperature 130° C. or higher, whereas the glass/polyamide compoundmaterial 2 undergoes only limited lowering of the modulus of elasticityat 250° C. or higher, thus testifying to the high thermal resistance ofthe glass/polyamide compound material 2.

[0065] From each of the three compound materials (compound materials 1to 3), a sheet was similarly prepared by a paper-makingtechnique andallowed to stand for 24 hours in an atmosphere of 25° C. temperature and95% relative humidity to cause approximately 5 weight % of the moistureto be absorbed into the sheet. The modulus of elasticity was measured bya vibration reed method to compare the modulus of elasticity before andfollowing the moisture absorption.

[0066] For comparison, fibrid composed only of a polyamide componentwere synthesized, and similar measurements were made of the sheetsprepared therefrom.

[0067] The results are shown in Table 1: TABLE 1 only compound compoundcompound polyamide material 1 material 2 material 3 component modulus of0.47 0.61 0.63 0.41 elasticity before moisture absorption GPa) modulusof 0.40 0.58 0.62 0.21 elasticity after moisture absorption (GPa) rateof change (%) 14.8 5.7 0 48.0

[0068] In the sheet formed only of a polyamide component, the physicalproperties are lowered appreciably. In the compound materials 1 to 3,the lowering of the physical properties as the result of moistureabsorption is decreased, thus indicating marked improvement inmoisture-proof property.

[0069] Preparation of the Loudspeaker

[0070] A loudspeaker cone was prepared by preparing a sheet of thecompound material 2 by a paper-making technique. Using a voice coil, avoice coil bobbin of which is formed by an aluminum foil, a full-rangespeaker, 16 cm in diameter, was prepared as Example 1.

[0071] Similarly, a loudspeaker cone as a diaphragm was prepared from apolypropylene/mica compound material to prepare a full-range loudspeaker16 cm in diameter as Comparative Example 1.

[0072] The loudspeakers, prepared as described above, were put to aninput resistance test based on EIJA testing standard. The testing timewas set to 100 hours.

[0073] The results are shown in Table 2. TABLE 2 Comparative Example 1Example 1 input (W) 40 60 80 40 60 80 time until breakdown (hrs) 100 100100 100 33 12

[0074] In the Comparative Example 1, heat evolved in the voice coil froman aluminum foil as a voice coil bobbin component is transmitted to thediaphragm so that the diaphragm was thermally deformed at inputs of 60and 80 W before the test time duration of 100 hours elapses such thatthe diaphragm/voice coil bonding point was destroyed.

[0075] Conversely, the loudspeaker, employing the compound material 2 asa diaphragm, remained thermally stable, without being destroyed, thustestifying to the high input resistance.

[0076] A loudspeaker cone as a diaphragm was then prepared from theglass/polyamide compound material 2. Using this loudspeaker cone, a 5 cmfull-range loudspeaker was prepared (Example 2) and allowed to stand inan atmosphere of the temperature of 25° C. and the relative humidity of95%. The frequency response before storage and that after storage weremeasured and compared to each other to check for the effect oftemperature.

[0077] For comparison, a loudspeaker cone as a diaphragm was preparedfrom a material composed only of the polyamide component and a similarloudspeaker was prepared (Comparative Example 2). The frequency responsebefore storage and that after storage were similarly measured andcompared to each other to check for the effect of temperature.

[0078] The results are shown in FIG. 2.

[0079] As may be seen from FIG. 2, changes in the frequency response aresignificant before and after moisture absorption in the ComparativeExample 2. Conversely, only small changes occur in the frequencyresponse before and after moisture absorption in the Example 2, thustestifying to appreciably improved moisture-proof property.

[0080] Investigations into Preparing a Sheet from a Mixed Material bythe Paper-making Technique

[0081] A mixed material of the glass/polyamide compound material 2 andthe pulp was formed into a sheet by a paper-making technique to checkfor the possibility of preparing a sheet from a mixed material withother materials routinely used in the paper-making technique.

[0082] Three mixed liquid dispersions with pulp amounts of 5 weight %,50 weight % and 95 weight % were prepared to check for the state ofliquid dispersion and the state of the sheets formed.

[0083] It was found that, in none of the mixed liquids, the tendency forseparation was observed. Similarly, in none of the sheets formed, theseparated state was observed.

[0084] From this it is seen that the sheets can be formed by thepaper-making technique from the material composed of a mixture withother materials routinely used in the conventional paper makingtechnique.

What is claimed is:
 1. A diaphragm for a loudspeaker comprising acompound material containing glass particles having a particle size of 8nm to 300 nm and a polyamide resin, said compound material being asheet-like member formed by a paper-making technique.
 2. The diaphragmfor the loudspeaker according to claim 1, wherein the content of saidglass particles in said compound material is 5 weight % to 70 weight %.3. The diaphragm for the loudspeaker according to claim 1, wherein saidsheet-like member is formed by the paper-making technique from a mixtureof said compound material with an other fiber material.
 4. The diaphragmfor a loudspeaker according to claim 3, wherein said other fibermaterial is pulp.
 5. The diaphragm for the loudspeaker according toclaim 3, wherein the proportion of said compound material in thesheet-like member formed by the paper-making technique is 5 weight %. 6.The diaphragm for the loudspeaker according to claim 1, wherein saidcompound material is fibrous.
 7. A method for preparation of diaphragmfor a loudspeaker comprising the steps of: contacting a phase of anaqueous solution containing diamine and water glass and a phase of anorganic solution containing a dicarboxylic acid halide to generate acompound material containing glass particles and a polyamide resin; andforming the resulting compound material to a shape of a diaphragm byapplication of a paper-making technique.
 8. The method for thepreparation of the diaphragm for the loudspeaker according to claim 7,wherein said phase of the aqueous solution and the phase of the organicsolution are subjected to an interfacial polycondensation reaction. 9.The method for the preparation of the diaphragm for the loudspeakeraccording to claim 7, wherein a diamine monomer contained in said phaseof the organic solution is one of 1,6-diaminohexane, m-xylenediamine andm-phenylene diamine.
 10. The method for the preparation of the diaphragmfor the loudspeaker according to claim 7, wherein an organic solventcontained in said organic solution phase is one of toluene, xylene,methylisobutylketone, chloroform, cyclohexane, cyclohexanone andtetrahydrofuran.
 11. The method for the preparation of the diaphragm forthe loudspeaker according to claim 7, wherein said water glass is 2 to100 g/l (liter) based on a solid content.
 12. The method for thepreparation of the diaphragm for the loudspeaker according to claim 7wherein the monomeric concentration of said aqueous solution phase andsaid organic solution phase is set to 0.1 to 1.2 mol/l.
 13. The methodfor the preparation of the diaphragm for the loudspeaker according toclaim 7, wherein the compound material produced is fibrous.